By good- I define, not a cheap, badly ported game from the PC(which it may have been brilliant on but didn't work for a controller)
I already played Halo Wars but want to play more and I can't get Starcraft 2 because my computer wont be able to run it.

Note: I have an Xbox 360

Hmm, if you had a PS3 i would recommend Valkyria Chronicles, that's pretty awesome, but also an exclusive And Battalion Wars for Gamecube worked pretty good too. Don't know any multiplatform or XBox ones, but atleast they prove they can exist

Tom Clancy's EndWar: If you can pull the trigger button and bark out orders then you have all the knowlage you need to play this game.